Conventional processes used in the creation and treatment of potable water vary depending upon the properties of the original, raw water source used as a supply. Whether from rivers, wells, aquifers, saltwater, natural or man-made reservoirs, the properties of the raw water supply can vary substantially based on geography even within short distances. Due to presence of e.g., both manmade and naturally occurring substances found in the earth at or near the raw water source and variations in such substances between different locations, substantially different processes may be required for water treatment.
By way of example, conventional treatment of surface water can include the application of various chemicals to achieve neutralization of harmful organisms and the coagulation or flocculation of undesired components that are then removed by filtration of the same. After filtration, the water may be potable but still have unacceptable values for pH, turbidity, hardness, and/or alkalinity. Thus, treatment before or after filtration may be required to affect these properties.
Even where raw water is provided from underground sources that are already potable, it may still have unacceptable values of pH, turbidity, hardness, and/or alkalinity. For example, water from underground aquifers typically has an unacceptable level of hardness. As such, further treatment for hardness is required to remove excessive amounts of minerals that will otherwise leave scale or undesirable deposits in piping and equipment. Treatment may also be required to obtain acceptable values for pH, turbidity, and/or alkalinity.
Another difficulty encountered with conventional water treatment processes is that steps required to positively treat one property can adversely affect other properties. For example, a current method for the treatment of water hardness in potable water includes large-scale, reverse osmosis (RO) systems. Reverse osmosis is a type of filtration that can remove undesired molecules and ions, along with other particulates, from water. Typically, water that is placed on one side of a membrane and by the application of pressure, water will move through the membrane leaving the undesired solutes and other particulates on the pressured side. The membranes used for reverse osmosis are selective in that such will not allow certain larger molecules and ions to pass through—thereby removing the same from the water.
Reverse osmosis is frequently used in the creation of potable water from seawater or saltwater. Removing the salt and other substances from the water is a necessary step in the creation of water suitable not only for human consumption but also for industrial applications where saltwater would foul pipes and otherwise introduce undesirable components. Depending upon the geographical location of a population center, saltwater may be the only practical source of water available in the quantities needed.
Unfortunately, the effectiveness of reverse osmosis actually creates a water quality problem. More specifically, in the removal of undesirable salts and other particulates, all or most dissolved minerals are also removed, some of which have desirable properties for potable water. For example, reverse osmosis can effectively remove mineral salts and other particulates from salt water to provide a water having an acceptable turbidity. However, the resulting water can also have unacceptably low values of pH, alkalinity, and hardness.
In order to improve pH, alkalinity, and hardness of the water from raw water sources or from treatment processes such as reverse osmosis that remove desirable minerals, various chemicals can be added in order to mineralize the water. One approach includes the addition of sodium hydroxide in order to adjust the pH. However, adding additional sodium can be counterproductive as it can adversely affect the taste of the water and contradicts certain recommendations of the World Health Organization. Also, the addition of sodium hydroxide does not improve alkalinity or hardness. Soda ash (sodium carbonate) can be used to raise pH and can improve alkalinity, but such does not improve the hardness of the de-mineralized water.
Another option to treat the de-mineralized water includes blending it with mineralized water provided from e.g., a non-membrane, water treatment process. By blending the two, the overall mineral content and pH of the de-mineralized water can be brought to acceptable ranges for potable water. Yet, this approach may not be economically feasible if, for example, the non-membrane water plant (mineralized water) is at great distances from the reverse osmosis water plant (de-mineralized water) or mineralized water is otherwise unavailable.
The addition of slaked lime (i.e. Ca(OH)2) to de-mineralized water can effectively raise pH, improve alkalinity, and add needed hardness to the water. Unfortunately, however, the solubility of slaked lime in water is very low at about 1 part per 1000 parts water and the time to reach complete saturation can occur very slowly. Thus, when lime is used to adjust pH, alkalinity, and hardness to the desired levels, turbidity is frequently increased to an unacceptable value. For example, a typical requirement is that potable water from e.g., reverse osmosis treatment must have less than 1 NTU of turbidity. The addition of slaked lime in quantities sufficient to positively affect pH, alkalinity, and hardness typically will typically also cause an unacceptable increase in turbidity to values of 2 or 3 NTU or higher.
Accordingly, a system that can effectively provide for the treatment of water would be useful. More particularly, a system that can provide for the treatment of water in order to improve pH, hardness, and alkalinity without raising the turbidity of the water above unacceptable levels would be very beneficial. Such a system that can operate e.g., with minimal or no blending and without adding sodium or other undesirable chemicals to the water would be also be desirable and useful.